add dnsname to netbox and differentiate dnsname and sysname

Today the netbox.sysname is in fact the dns name, of this fails to loop up, the ip address. the mib2 system.sysname is not used (it used to be a long time ago). By adding a new field to the netbox table we can collect both values. It should be admin configurable (in nav.conf) which name to present as default in the web face (ip device center can present both).
In addition syslocation, syscontact and possible other system variables should be collected and added as new fields to the netbox table,